The present invention relates to an internal step-down power supply circuit suitable for use in a semiconductor device.
An internal step-down or deboost power supply circuit for generating an internal source or power-supply voltage by using an external power-supply voltage comprises a driver for supplying a source or power supply voltage, a divider circuit for dividing the internal power-supply voltage, an amplifier for comparing the voltage generated from the divider circuit and a reference voltage and supplying a drive voltage to the driver based on the result of comparison, etc.
Now, the more a circuit connected to a terminal for outputting an internal power-supply potential in the internal step-down power supply circuit increases in size, the more source impedance must be reduced. Thus, the size of a transistor for the driver becomes very large in a VLSI in which a stepped-down or deboosted power supply produced in the internal step-down power supply circuit is used in the whole semiconductor chip, thereby increasing load capacity of the amplifier. However, a change in instantaneous current of the circuit connected to the terminal for outputting the internal power-supply potential results in such very large values as to rise in one stroke from a value near zero to a few 10 mA even in the case of a small current and a few 100 mA in the case of a large current. On the other hand, since the current that the amplifier can feed, is limited in terms of specs, various methods used up to now could not achieve compatibility with a follow-up to a change in internal step-down power-supply potential.
An object of the present invention is to provide an internal step-down power supply circuit which is capable of improving response performance (transition from a standby state to an active state in particular) of a system without increasing current consumption.
An internal step-down power supply circuit of the present invention includes an internal step-down power supply output node for outputting an internal step-down power-supply potential, a driver for adjusting an external power-supply potential and outputting the same to the internal step-down power-supply output node, a divider circuit for diving a voltage developed at the internal step-down power-supply output node and outputting a divided voltage, and a differential amplifier for comparing the voltage outputted from the divider circuit and a reference voltage and outputting a voltage equivalent to twice the predetermined gain, the operational amplifier setting the conductance of each of transistors for feeding a current in response to the reference voltage to twice or more the conductance of each of transistors for feeding a current in response to the voltage outputted from the divider circuit.